In the reference technical sector it is known that, to maintain efficient combustion, it is necessary for the ratio between the amount of air and the amount of fuel gas introduced into the burner to be maintained at around a predetermined optimal value, which depends substantially on the type of gas used and, in general, can also depend on the value of the power delivered by the burner, i.e. by the gas flow rate.
In this way a complete combustion process can be achieved and maintained over time without excessive energy loss as fumes, while minimising the production of polluting gases and complying with emissions legislation in the various countries.
To achieve this objective of maintaining the optimal air/gas ratio, various devices and methods have been developed in the reference technical sector.
In the specific scope of the invention, there are known methods for monitoring and controlling combustion on the basis of flame analysis and, in particular, analysis of the gas ionisation in the combustion zone of the flame. Typical methods provide for the use of an electrode which is placed in or close to the flame zone and connected to an electronic circuit that applies a fixed or variable voltage to the electrode and measures the current passing through said electrode. One or more combustion-related parameters are estimated by means of systems for processing and analysing the current signal. The processing systems include known methods for analysing the frequency spectrum of the signal, which analysis is capable of identifying frequency spectra or variations of the same that indicate flame instability or sub-optimal combustion, on the basis of which, systems for correcting the combustion are provided in order to return the latter to the desired conditions.
Identifiable limitations of the known methods relate mainly to the reliability of the results of the frequency spectrum analyses and to their correlation with the combustion process.
Limitations can also be encountered in the possible wear and ageing of the electrode for receiving the signal in the ionisation sensor, with consequent repercussions on the reliability and accuracy of the data analysed by the frequency spectrum processing algorithms.
The aforesaid limitations are also amplified if the combustion control is to be carried out in burners of the modulating type, in which optimal combustion conditions are sought by varying the required power, within the range between minimum power and maximum admissible power for the burner.
It is also known that the volumetric ratio between the gas flow rate and the air flow rate appropriate for correct combustion also depends on the type of gas. Therefore, each family of fuel gases is correlated with respective, specific control curves (which, for example, correlate the gas flow rate with the air flow rate). One of the problems of known systems for controlling combustion consists is identifying the family of gases and associating the optimal control curves.